Mobile communication systems continue to grow in popularity and have become an integral part of both personal and business communications. Various mobile devices now incorporate Personal Digital Assistant (PDA) features such as calendars, address books, task lists, calculators, memo and writing programs, media players, games, etc. These multi-function devices usually allow electronic mail (email) messages to be sent and received wirelessly, as well as access the internet via a cellular network and/or a wireless local area network (WLAN), for example.
Some mobile devices incorporate contactless card technology and/or near field communication (NFC) chips. NFC technology is commonly used for contactless short-range communications based on radio frequency identification (RFID) standards, using magnetic field induction to enable communication between electronic devices, including mobile wireless communications devices. This short-range high frequency wireless communications technology exchanges data between devices over a short distance, such as only a few centimeters. Typical NFC chips operate in one of three modes: an integrated circuit (IC) card emulation mode (NFC device appears to an external reader as a traditional contactless smart card); a reader/writer mode (NFC device reads NFC tags); and a peer-to-peer mode (two NFC devices exchanging data).
Referring to FIG. 1, a typical NFC device 10 includes an NFC IC chip 11, an NFC antenna 12, and a coupling circuit 13 coupled between the NFC IC chip and the NFC antenna. The NFC antenna 12 is modeled to include a resistor 71 (RS), an inductor 72 (LS) coupled in series thereto, and a capacitor 73 (CA) coupled in parallel to the resistor and the inductor. The coupling circuit 13 illustratively includes a tuning circuit comprising a first capacitor 61 (CAC2), a second capacitor 62 (CAC1) coupled in parallel to the first capacitor, and a diode 63 (DAC1) coupled in series to the second capacitor. The coupling circuit also includes a receive branch including a resistor 65 (RR), and a capacitor 66 (CR) coupled in series thereto, and an antenna branch including an inductor 67 (LE), and a pair of capacitors 68-69 (CE,C) coupled thereto. Drawbacks to this NFC device 10 may include heavy loading of the external circuit to the NFC resonating tank, thereby reducing the Q factor of the NFC antenna 12. Moreover, the different operating modes of the NFC IC chip 11 may not be optimized, and it may be difficult to match and tune each coupling branch without unintentional cascaded effects.